And, importantly, there already is an official diff tool: the "Compare" button.
https://theredline.versionstory.com/p/on-building-git-for-la...
Wouldn't the obvious solution then be to take the tool they already use for redlining (e.g. Word's compare function) and integrate it into a git workflow?
[1] https://stackoverflow.com/questions/12356917/how-to-set-diff...